Lubricant for run flat tire system

ABSTRACT

Lubricant compositions as well as methods and articles utilizing the lubricant compositions that comprise a polyoxyalkene as a lubricating agent, between 4 wt. % and 7.5 wt. % of silica as a thickening agent and an inorganic thixotropic-enhancing metal compound added in an amount of, for example, at least 20 ppm, by weight or alternatively, between 1 ppm and 2 wt. %. The silica may be fumed silica. Examples of the metal compound include KOH, NaOH, KCl, CaCl 2 , MgCl 2 , CaO, MgO, Mg(OH) 2  or combinations thereof. A tire is also included, comprising a radially inner face designed to be opposite a wheel rim on which it is designed to be mounted, wherein the radially inner face is provided with the lubricant composition described above.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to lubricants and more particularly, tolubricant compositions and methods for their use in a run-flat tiresystem.

2. Description of the Related Art

Run-flat tire systems have been developed to provide tires for vehiclesthat can be operated in a deflated condition for a suitable distance ata desired speed. Such systems have provided significant benefits tovehicle operators including safety benefits that are realized when, forexample, a vehicle can continue traveling with a deflated tire underconditions that are not safe for changing the tire at the side of aroad. Thus, run-flat tire systems improve the safety of the vehicle byallowing the vehicle to continue to travel for a certain time until asuitable place for repairs can be found.

Run-flat systems having safety support rings are well known. U.S. Pat.No. 6,944,948 of Pompier, which has been assigned to Michelin Rechercheet Technique, discloses such a system. Pompier discloses a run-flat tiresystem having a safety support ring consisting of a circular bodyadapted for fitting onto a wheel rim of a vehicle. The disclosed safetysupport ring is comprised of a vulcanized rubber mix and includes areasthat are reinforced by, for example, metallic or textile wires orcables. While Pompier discloses a safety support ring made of avulcanized rubber mix, the support rings are not so limited and may bemade, for example, of plastics such as polyurethane.

Such safety support rings are generally mounted on a wheel rim inside atire to provide support for the crown of the tire when it is rolling atlow or zero pressure. The safety support ring is meant to prevent directcontact between the tire and the wheel rim because such contactgenerally results in rapid deterioration of the tire.

To improve rolling under the condition of low or zero pressure, it ispreferable to provide lubrication at the interface between the insidesurface of the tire and the surface of the support ring. Suchlubrication promotes extended durability in the friction zones that aresubjected to relatively high temperatures due to the friction betweenthe surfaces if no lubrication is provided.

One example of a lubricant composition that has been used forlubricating the interface between the inside surface of a tire and thesurface of a safety support ring is disclosed in U.S. Pat. No. 6,750,181of Salaun, et al, which has been assigned to Michelin Recherche etTechnique. The lubricant composition disclosed by Salaun includes anaqueous or nonaqueous lubricating agent and a polysaccharide intended tothicken the lubricating agent and impart a thixotropic property to thelubricant.

As known to those having ordinary skill in the art, a thixotropicmaterial is a pseudoplastic non-Newtonian fluid that, after undergoingshear thinning, has the potential to have its structure reformed whenallowed to rest over a period of time. A pseudoplastic fluid has aviscosity that decreases as the applied shear rate increases and thatdecreases at a constant applied shear rate. The process of applying ashear rate to decrease viscosity is called shear thinning. Therefore, athixotropic material that is a gel, for example, may become afree-flowing liquid when subjected to shear thinning but upon thecessation of the applied shear rate, the structure of the material mayreform and convert back to a gel over time as the material rests.

Another example of a lubricant composition that has been used in arun-flat tire system is disclosed in U.S. Patent Publication No.2002/0016535 of Mauclin, et al., which has been assigned to MichelinRecherche et Technique. Mauclin discloses a lubricating composition thatincludes a lubricating agent and a thickening agent, the preferredlubricating agents being a polyoxyalkene with between 4 wt. % and lessthan 7.5 wt. % fumed silica as the thickening agent.

Generally, the lubricant compositions of the run-flat tire system may beapplied to the surface of the safety support ring (if a safety supportring is part of the run-flat tire system), the inside surface of thetire or both. The thickening agent added to the lubricant composition isintended to increase the viscosity of the lubricating agent so as tominimize the flowing of the lubricating agent due to its weight when thevehicle is at rest or is traveling with its tires inflated.

SUMMARY OF THE INVENTION

The present invention provides lubricant compositions as well as methodsfor their making and their use and articles that use the lubricantcompositions. In a particular embodiment of a lubricant composition ofthe present invention, the lubricant composition comprises apolyoxyalkene as a lubricating agent, between 4 wt. % and 7.5 wt. % ofsilica as a thickening agent and an inorganic thixotropic-enhancingmetal compound. The metal compound may, for example, be added inparticular embodiments in an amount of at least 20 ppm, by weight oralternatively, between 1 ppm and 2 wt. %. The silica may be a fumedsilica.

In particular embodiments of the present invention, the metal componentof the thixotropic-enhancing metal compound may be selected from alkalimetals, alkaline earth metals or combinations thereof. Likewise, theanion associated with the thixotropic-enhancing metal compound may beselected from chlorides, hydroxides, sulfides, oxides or combinationsthereof. Examples of the metal compound include KOH, NaOH, KCl, CaCl₂,MgCl₂, CaO, MgO, Mg(OH)₂ or combinations thereof.

Particular embodiments of the present invention include thepolyoxyalkene as a polyoxyalkene glycol and embodiments include thepolyoxyalkene having an alkene portion selected from ethylene,propylene, butylene or combinations thereof.

Particular embodiments of the present invention further include a tirecomprising a radially inner face designed to be opposite a wheel rim onwhich it is designed to be mounted, wherein the radially inner face isprovided with the lubricant composition described above.

Additional embodiments include a lubricant composition comprising alubricating agent selected from glycerol, polyalkylene glycol orcombinations thereof, an organoclay and a viscosity-enhancing inorganicmetal compound. The viscosity-enhancing inorganic metal compoundsinclude the same compounds as described above as thixotropic-enhancingcompounds. However, these compounds surprisingly increase the TS1properties of the lubricant composition and hence, they are identifiedas viscosity-enhancing compounds in those embodiments of the presentinvention that include organoclay as the thickening agent.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of particular embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-E are graphs of the shear rate plotted against the shear stressobtained from a cone-plate rheometer to determine the initial thresholdstress value TS1 and the recovered threshold stress value TS2 oflubricant compositions having fumed silica as a thickening agent anddiffering thixotropic-enhancing metal compounds.

FIGS. 2A-C are graphs of the shear rate plotted against the shear stressobtained similarly to FIGS. 1A-E demonstrating the difference betweenlubricating agents used in lubricant compositions.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention includes a lubricant composition useful forlubricating the interface between the inside of a tire and the surfaceof a safety support ring for a run-flat tire system. The inventionfurther includes run-flat tire systems having safety support rings aswell as those that are designed to operate without safety support rings,both using such lubricant compositions. The invention further includesmethods for using and making such lubricant composition.

In particular embodiments of the present invention, a lubricantcomposition is provided that includes a lubricating agent, a thixotropicthickening agent that thickens and imparts a thixotropic character tothe lubricant composition and an inorganic thixotropic-enhancing metalcompound. The addition of even a small amount of the inorganic metalcompound advantageously not only increases the viscosity of thelubricant composition but quite surprisingly, typically increases thethixotropic properties of the composition.

Non-limiting examples of metals included in the inorganicthixotropic-enhancing metal compound include, for example, the alkalimetals, the alkaline earth metals, iron, cobalt, nickel, aluminum,copper, zinc and combinations thereof. The more suitable metals arethose that have a +1 or +2 valence state.

Non-limiting examples of the anion associated with the inorganicthixotropic-enhancing metal compound include, for example, chlorides,hydroxides, sulfides and oxides. The more suitable anions are thosehaving a −1 or −2 valence state.

Particular embodiments include, for example, inorganicthixotropic-enhancing metal compounds such as KOH, NaOH, KCl, NaCl,MgCl₂, CaO, MgO and combinations thereof.

To increase the viscosity of the lubricant composition and increase itsthixotropic properties, the inorganic thixotropic-enhancing metalcompound is added in an amount of at least about 1 ppm or alternatively,at least about 50 ppm or at least 20 ppm. Particular embodiments of thepresent invention include an amount of inorganic thixotropic-enhancingmetal compound of between about 1 ppm and about 2 wt. %, of between 10ppm and 1 wt. %, of between 10 ppm and 800 ppm, of between 50 and 700ppm or alternatively, between about 100 ppm and about 700 ppm.

Non-limiting examples of suitable lubricating agents include diols,triols, tetrols, polyhydric alcohols, glycol ethers, glycerin ormixtures thereof. Particular embodiments have lubricating agents thatinclude one or more polyoxyalkylenes, especially polyalkylene glycols.Examples of preferred polyalkylene glycols include polyethylene glycol,polypropylene glycol, polybutylene glycol or mixtures thereof.

Particular embodiments of the lubricant composition include a copolymerthat is a mixture of alkylene oxides, and more particularly, mixtures ofethylene oxide and propylene oxide polymers. Particular embodimentscomprise units resulting from ethylene oxide in a preferred molefraction of between about 40% and about 80% (alternatively between about50% and about 70%), and units resulting from propylene oxide in a molefraction of between about 20% and about 60% (alternatively, betweenabout 30% and about 50%). When selecting a polyalkylene glycollubricating agent, consideration should be given to hygiene issues suchas those disclosed in the literature, e.g., ECETOC, European Centre forEcotoxicology and Toxicology of Chemicals, Technical Report No. 55,Pulmonary Toxicity of Polyalkylene Glycols, Brussels, December 1997,ISSN-0773-8072-55.

Particular embodiments of the lubricant composition include lubricatingagents that may be characterized as having an apparent viscosity ofbetween about 100 and about 2,000 centipoise (1 centipoise=1 mPa·s) andmore particularly between about 500 and about 1,600 centipoise whenmeasured at 23° C. in accordance with European and Internationalstandard EN ISO 2555 (June 1999) (viscosity by the Brookfield method;rotating viscometer of type A; rotation speed 20 RPM; mobile No. 2;model RVT).

Particular embodiments of the present invention further include apolyoxyalkene having a number-average molecular weight (Mn) between1,000 and 10,000 g/mol or alternatively between 2,000 and 6,000 g/mol.Furthermore, the polymolecularity index (Ip) of particular embodimentsis less than about 1.5 or alternatively, less than 1.3, wherein Ip=Mw/Mnwhere Mw is the weight-average molecular weight.

Examples of suitable ethylene oxide and propylene oxide copolymerlubricating agents that are available commercially include SYNALOX40D300 and UCON 75H1400, which are available from Dow Chemical Company;BREOX 60W460 and BREOX 60W320, which are available from CognisCorporation having offices in Cincinnati, Ohio; and CLARIANT D21/300,which is available from Clariant Corporation having offices inCharlotte, N.C. Other suitable copolymers include, for example, EMKAROXVG 217W, EMKAROX VG 379W, EMKAROX VG 650W and EMKAROX VG 1051W, allavailable from Uniqema, with offices in Delaware.

In particular embodiments of the lubricant composition, glycerin is usedas the lubricating agent. A suitable glycerin for use in the presentinvention is commercially available under the trade name SUPEROL fromProcter & Gamble, Cincinnati, Ohio. SUPEROL is 99.7% pure glycerol andproduces a superior lubricant composition as compared to STAR glycerin,also a Procter & Gamble product, which is only 96% pure glycerol.

The lubricant composition should be compatible with all the componentsof the run-flat tire system in which the lubricant composition is beingused. Such components of the run-flat system may include, for example,the tire, the safety support ring, the wheel, the electronic pressuremonitor and any chemicals or lubricants applied separately to these orother components.

For example, the lubricant composition should be compatible with any ofthe materials that may be used for the inside of the tire and/or for thesafety support ring. Preferred materials for the safety support ringinclude, for example, natural and synthetic rubbers as well as polymerssuch as polyurethane or thermoplastic elastomer (TPE). These materials,as well as the other components of the run-flat tire system, should besubjected to an aging test with the lubricant composition to determinetheir compatibility by using methods known to those having ordinaryskill in the art. A lubricant-free control sample of each materialshould also be subjected to an identical aging test for comparison.Material measurements—notably weight, dimensions, Shore hardness, andtensile strength—should be made before and after the aging test. Changesto the critical characteristics of the materials caused by lubricantincompatibility may alter the performance and/or acceptability of thesystem. Such changes may include, for example, swelling, shrinking,hardening, softening, becoming more or less brittle and/or changingcolor.

Particular embodiments of the present invention include the lubricantcomposition having a thixotropic agent that both thickens thecomposition and imparts or improves the thixotropic property of thecomposition.

The desired thixotropic properties of the present invention may becharacterized by the initial threshold stress value (TS1) of thelubricant composition and by the recovered threshold stress value (TS2)of the lubricant composition, which is determined after the lubricantcomposition has undergone a set amount of shear stress and then allowedto recover. The procedure for measuring the TS1 and the TS2 thresholdstress values of a lubricant composition is provided in Example 3 of theexamples section that follows.

The desired thixotropic properties of the present invention provide alubricant composition that does not flow under its own weight when atrest, that does not flow well when subjected to shear stress levels thatare less than TS1, and that upon cessation of the shear stress, returnsto a form having a TS2 that is at least 50% of TS1. In particularembodiments of the present invention, the material returns to a TS2 thatis within at least 25% of TS1 and alternatively, within at least 10% ofTS1. Particular embodiments of the present invention include a lubricantcomposition having a TS2 that is within at least 5% if TS1 oralternatively, between 3% of TS1 and TS1 itself. Thus, particularembodiments of the present invention include lubricant compositions thathave a TS2 that is substantially the same as TS1, which means that TS1and TS2 are measured as the same within the error of the measuringdevices and method. In particular embodiments of the present invention,the lubricant composition has a initial threshold stress TS1 greaterthan about 50 Pa and in others, greater than about 150 Pa. Particularembodiments include a range for TS1 of between about 200 and about 600Pa and others, between about 275 and about 475 Pa.

High threshold stress values of the lubricant composition are desiredbecause they relate to maintaining the balance of the lubricantcomposition in the tire. Vehicle operators demand that the tires ontheir cars perform at a minimum level of noise and vibration. If thelubricant composition moves around inside the tire during normaloperation, the balance of the tire may become affected and cause thetire to become unbalanced, thereby causing excessive noise andvibration.

Viscosity of the lubricant composition may be controlled by adjustingthe amount of lubricating agent in the lubricant composition. Though notlimiting the invention, particular embodiments of the lubricantcomposition of the present invention have a viscosity of between about10 and about 60 Pa·s and preferably between about 20 and about 50 Pa·sat 20° C. under a shear rate of 10 s⁻¹ as measured on a cone and platerheometer.

Those having ordinary skill in the art may adjust the amount oflubricating agent according to the particular nature and geometry of thesafety support ring or other components of the particular run-flatsystem in order to avoid the risks due to excessively high orexcessively low fluidity of the lubricant composition. The risksassociated with excessively high fluidity include the parasitic drainageof the lubricant composition while at rest, which may causewheel-balance problems during subsequent normal operating conditions,i.e., at normal inflation pressure. The risks associated withexcessively low fluidity include the non-uniform distribution of thelubricant composition around the safety support ring during flat runningoperating conditions, which would typically cause an adverse effect onthe overall endurance of the tire and safety support ring.

Particular embodiments of the present invention provide a lubricantcomposition that possesses the desired thixotropic and lubricantproperties when operating over a wide range of outside weathertemperatures such as, for example, between about −40° C. and about 55°C.

The thickening agent may be selected from a polysaccharide, anorganoclay or silica. Each of these thickening agents imparts at leastsome thixotropic properties to the lubricant composition of the presentinvention, with the organoclay imparting the greatest amount. It shouldbe noted that when an organoclay is used as the thickening agent, thethixotropic properties are already so high that the addition of themetal compound typically does not increase the thixotropic propertiesalthough the addition surprisingly does increase the TS1 and TS2. Thepolysaccharide in particular embodiments of the present invention is axanthan gum. Particular embodiments of the present invention include thepolysaccharide in an amount of between about 1 wt. % and about 2 wt. %.

Those embodiments having silica as the thickening agent may include anysilica known to those having ordinary skill in the art. Particularembodiments include fumed silica, especially those having BET and CTABsurface areas below about 450 m²/g. Particular embodiments include a BETsurface area of between 50 and 350 m²/g or alternatively, between 100and 250 m²/g. Particular embodiments having a safety support made of adiene elastomer, such as natural rubber, or from a polyurethaneelastomer may include, for example, fumed silica as the thickening agenthaving a BET of between 100 and 250 m²/g.

In the present description of the silica, the BET specific surface area(“area per unit mass”) is determined by gas adsorption using theBrunauer-Emmett-Teller method described in “The Journal of the AmericanChemical Society”, Vol. 60, p. 309, February 1938, and more precisely inaccordance with French standard NF ISO 9277 of December 1996 [multipointvolumetric method (5 points)—gas: nitrogen—degassing: 1 hour at 160°C.—relative pressure range p/p_(o): 0.05 to 0.17]. The CTAB specificsurface area is the external surface area determined in accordance withFrench standard NF T 45-007 of November 1987 (method B).

Particular embodiments of the lubricant composition according to theinvention having silica include the silica in an amount that must behigher than 4.0% and lower than 7.5%, otherwise the endurance levelsduring flat running required for the mounted assemblies of the inventionare not reached. For that reason, the proportion of silica in particularembodiments is between 5.3 wt. % and 6.7 wt. % or alternatively between5.5 wt. % and 6.5 wt. %. A mass fraction of silica equal to about 6.0wt. % (e.g., 6.+−.0.3%) has been used in numerous embodiments of thepresent invention.

Advantageously, the lubricant composition having silica as thethickening agent does not require the presence of water, which favorsthe interaction of the lubricating agent (polyoxyalkene) with thethickening agent (silica). It is for this reason that it can be called“non-aqueous” or of the non-aqueous type, even though it can toleratethe presence of a small amount of water without ill effect. Embodimentsof the present invention are “non-aqueous” compositions having silica,which is understood to mean compositions containing less than 2 wt. % oralternatively leis than 1 wt. % of water (% by weight of the lubricantcomposition).

Particular embodiments of the invention having an organoclay as thethickening agent include a mineral clay mixture that has been treatedwith an alkyl quaternary ammonium compound and comprises sepiolite,palygorskite or mixtures thereof. Particular embodiments include amineral clay mixture that has been treated with an alkyl quaternaryammonium compound includes at least one of sepiolite, palygorskite and asmectite with between about 50-100 wt. % sepiolite, palygorskite or amixture of sepiolite and palygorskite, the balance smectite.

An example of an organoclay suitable for use as the thixotropicthickening agent is commercially available under the trade name GARAMITEfrom Southern Clay Products, Gonzales, Tex. The GARAMITE organoclaycomprises a clay mixture that has been treated with a quaternaryammonium compound, preferably an alkyl quaternary ammonium salt, 50-95wt. % sepiolite, palygorskite or a mixture of the two, with the balanceof the clay mixture being smectite, as set forth in U.S. Pat. No.6,036,765.

In particular embodiments of the present invention, the organoclay isadded to the lubricant composition in an amount that is at least 5 wt. %of the total weight of the lubricant compound, between about 10 and 30wt. % or between about 3 and 40 wt. %. Particular embodiments of thepresent invention include adding the organo clay in an amount that isless than about 40 wt. % or less than about 30 wt. % of the total weightof the lubricant composition.

In particular embodiments of the present invention, the lubricantcomposition may include one or more additives such as, for example,antioxidants, coloring compounds, bactericides, ionic, non-ionicsurfactants or mixtures thereof. The total content of such additives inthe lubricant composition is preferably, but not limited to, less thanabout 2 wt. %. Particular embodiments of the present invention furtherinclude drying the organoclay before incorporating it into the lubricantcomposition.

The invention is further illustrated by the following examples, whichare to be regarded only as illustrations and not delimitative of theinvention in any way.

EXAMPLE 1

This example provides a procedure for mixing the components of thelubricant composition having silica as the thickening agent.Approximately 6 g of the fumed silica (CAB-O-SIL M5, manufactured byCabot Corp. of Tuscola, Ill.), approximately 93.9 g of a lubricatingagent (EMKAROX VG 379W, a 50/50 copolymer of PEG/PPG, available fromUniqema) and approximately 0.1 g of a 50-50 wt. % solution of thethixotropic-enhancing metal compound in water were measured outseparately and combined by hand mixing to make a lubricant compositionhaving 6 wt. % fumed silica. If the thixotropic-enhancing metal compoundwas not soluble in water, e.g., MgO, approximately 0.05 g of the solidmaterial was added without the water. The components of the preparedsamples are shown in Table 1.

The thixotropic-enhancing metal compound was added to the lubricatingagent and then the fumed silica was added to the lubricating agent infourths and mixed in a Kitchen Aid commercial mixer on the stirringspeed. The mixer was then stopped so that the sides could be scrapeddown towards the center of the bowl. The composition was then mixed fora total time of 30 minutes.

It should be noted that even though the lubricating agent was purchasedunder the same product properties, there may be differences in physicalproperties of the lubricating agents from batch to batch. Therefore, thelubricating agents disclosed in Table 1 are identified as batch (1) andbatch (2). It should also be noted that the amount ofthixotropic-enhancing metal compound disclosed in Table 1 is half thesolution added to the lubricant composition sample since the solution ofmetal compound was 50% water for those compounds added as a solution.

Once the lubricant composition had been mixed, the lubricant compositionwas allowed to rest in a desiccator for about 12 hours to deaerate. Oncethe air bubbles had escaped, the lubricant composition was ready fortesting to determine TS1 and TS2, as described in Example 3 below. Theresults of the testing to determine TS1 and TS2 are shown in Table 1.

TABLE 1 Components of Lubricant Composition Samples Thickened with FumedSilica Metal Silica, Metal Comp. TS1 TS2 Thixotropic Lubricating Agentwt. % Comp. ppm Pa Pa Recovery, % Sample 1 EMKAROX VG 379W (1) 6 None 0239 189 79 Sample 2 EMKAROX VG 379W (1) 6 KCl 500 312 306 98 Sample 3EMKAROX VG 379W (1) 6 MgCl₂ 500 536 474 88 Sample 4 EMKAROX VG 379W (1)6 MgO 500 286 263 92 Sample 5 EMKAROX VG 379W (1) 6 NaOH 500 482 461 96Sample 6 EMKAROX VG 379W (2) 6 None 0 108 48 43 Sample 7 EMKAROX VG 379W(2) 6 KCl 500 283 258 91 Sample 8 EMKAROX VG 379W (2) 6 MgCl₂ 500 525510 97

As shown in Table 2, adding just a small amount of thethixotropic-enhancing metal compound increased the thixotropic propertyof the lubricant composition from a recovery of 79% to a recovery offrom 88-98% of the starting TS1. The results of the second batch oflubricating agent demonstrated an even larger increase of thethixotropic properties with an increased recovery from 43% without thethixotropic-enhancing compound to 91-97% recovery.

EXAMPLE 2

This example provides a procedure for mixing the components of thelubricant composition having the organoclay as the thickening agent. Ingeneral, a higher shear and longer mixing times are required, ascompared to some known lubricant compositions, to ensure good dispersionof the organoclay throughout the composition.

Approximately 24 or 26 g of an organoclay (GARAMITE 1958), approximately174 or 176 g of a lubricating agent (SYNALOX 40D300) and approximately0.1-0.5 g of a 50-50 wt. % solution of the metal compound in water weremeasured out separately and combined by hand mixing to make a lubricantcomposition having 12 or 13 wt. % organoclay. The components of theprepared samples are shown in Table 2. It should be noted that whilesome of the samples showed an increase in the thixotropic properties,the thixotropic properties were already very high and most of thesamples showed only a slight or a negative change in thixotropicproperties. However, surprisingly, the addition of the metal compounddid increase the TS1.

The metal compound was added to the lubricating agent and then theorganoclay was added to the lubricating agent in fourths and mixed untilno powder was visible. The mixture was then mixed at 1000 RPM in anoverhead mixer (LIGHTNIN Model L1U08F) for 15 minutes. The mixer wasthen stopped so that the sides could be scraped down towards the centerof the bowl. The composition was then mixed for 5 minute periods at 1000RPM with the bowl scraped towards the middle after each period until thetotal mixing time had reached about 30 minutes.

TABLE 2 Components of Lubricant Composition Samples Thickened withOrganoclay Organoclay, Metal batch #, Metal Comp. TS1 Lubricating Agentwt. % Comp. ppm Pa Sample 1 SYNALOX 40D300 Clay 1, 12 None 0 94 Sample 2SYNALOX 40D300 Clay 1, 12 NaOH 1500 179 Sample 3 SYNALOX 40D300 Clay 2,12 None 0 170 Sample 4 SYNALOX 40D300 Clay 2, 12 MgCl₂ 500 184 Sample 5SYNALOX 40D300 Clay 2, 12 CaCl₂ 500 200 Sample 6 SYNALOX 40D300 Clay 2,12 NaOH 1500 321 Sample 7 SYNALOX 40D300 Clay 2, 13 NaOH 2500 722

It should also be noted that the amount of metal compound disclosed inTable 2 is half the solution added to the lubricant composition samplesince the solution of meal compound was 50% water.

Once the lubricant composition had been mixed, the lubricant compositionwas allowed to rest for about 24 hours to allow the lubricantcomposition to restructure. The lubricant composition was then ready fortesting to determine TS1 as described in Example 3 below.

As shown in Table 2, adding a small amount of the metal compound doessurprisingly increase TS1.

EXAMPLE 3

This example provides the procedure for measuring the threshold stressvalue of a lubricant composition including both the initial thresholdstress value (TS1) and the recovered threshold stress value (TS2) thatis measured after the composition has been subjected to an amount ofshear stress, as set in the procedure that follows, and then allowed torecover.

The rheological properties were measured on the THERMO HAAKE RheoStresslcone-plate rheometer with a 35 mm diameter titanium cone having 4degrees of angle and a truncation of 0.143 mm. The tests were typicallyrun at 20° C.

A sample of the lubricant composition measuring approximately 1.5 g wasplaced on the center of the plate of the rheometer. The cone partdescended rapidly until the gap between the plate and the cone was lessthan about 6 mm. The cone part slowed its descent at that point to about0.2 mm/min to avoid shearing the sample too much and to avoidintroducing air bubbles in the sample. After the working gap (0.143 mm)was reached, any excess sample was carefully removed with a spatula fromthe border of the cone to ensure that no lubricant composition remainedon the sides of the cone.

The sample was subjected to a controlled shear rate of 0.5 s⁻¹ for aperiod of 200 seconds. The sample was then allowed to rest for 600seconds. The rheometer then applied an initial shear stress of 1.0 Paand linearly increased the shear stress to 1000 Pa over a 1000 secondperiod. The shear stress was recorded as a function of the shear rateover this period of time. FIGS. 1A-E are graphs of the shear rateplotted against the shear stress obtained from the rheometer during theprocedure. The initial threshold stress values TS1 of the lubricantcompositions as shown in FIGS. 1A-E, as well as the other figures, weredetermined by obtaining the X=0 intercept by linear regression analysisof the stress versus shear rate between the shear rate values of 0.7 and1.5 s⁻¹. The initial threshold stress values for the lubricantcomposition samples are shown in Tables 1 and 2.

The sample was then allowed to rest for 600 seconds without any shearapplied and then the sample was subjected to a controlled shear rate of0.3 s⁻¹ for 300 seconds during which time the viscosity of the samplewas measured. Viscosities were then typically measured at 0.3, 1, 3 and10 s⁻¹ and then again at 3 s⁻¹ as a final measurement. Taking theseviscosity readings subjected the lubricant composition to stress so thata recovered threshold stress value TS2 of the worked lubricantcompositions could be measured after the viscosity readings wereobtained.

To determine the recovered threshold values TS2 of the lubricantcompositions after being subjected to the shear forces during theacquisition of the viscosity measurements, the lubricant compositionswere subjected to a linear controlled stress increase from 1 Pa to 600Pa over a 700 second period. The same method using linear regressionanalysis was then used to determine TS2 as was used to determine TS1.The results are shown as TS2 on the attached figures and in Tables 1 and2.

The terms “comprising,” “including,” and “having,” as used in the claimsand specification herein, shall be considered as indicating an opengroup that may include other elements not specified. The term“consisting essentially of,” as used in the claims and specificationherein, shall be considered as indicating a partially open group thatmay include other elements not specified, so long as those otherelements do not materially alter the basic and novel characteristics ofthe claimed invention. The terms “a,” “an,” and the singular forms ofwords shall be taken to include the plural form of the same words, suchthat the terms mean that one or more of something is provided. The terms“at least one” and “one or more” are used interchangeably. The term“one” or “single” shall be used to indicate that one and only one ofsomething is intended. Similarly, other specific integer values, such as“two,” are used when a specific number of things is intended. The terms“preferably,” “preferred,” “prefer,” “optionally,” “may,” and similarterms are used to indicate that an item, condition or step beingreferred to is an optional (not required) feature of the invention.

It should be understood from the foregoing description that variousmodifications and changes may be made in the preferred embodiments ofthe present invention without departing from its true spirit. Theforegoing description is provided for the purpose of illustration onlyand should not be construed in a limiting sense. Only the language ofthe following claims should limit the scope of this invention.

1. A lubricant composition, comprising: a polyoxyalkene as a lubricatingagent; between 4 wt. % and 7.5 wt. % of silica as a thickening agent; nomore than 1% water; and between 300 ppm and 2 wt. % of an inorganicthixotropic-enhancing metal oxide, wherein a metal component of thethixotropic-enhancing metal oxide is selected from alkali metals,alkaline earth metals, iron, cobalt, nickel, copper, aluminum orcombinations thereof, wherein the lubricant composition viscosity isbetween 10 Pa-s and 60 Pa-s measured at 20° C. with a shear rate of 10s⁻¹, and wherein the inorganic thixotropic-enhancing metal oxideprovides an increase in a recovered threshold stress value TS2 of thelubricant composition to at least about 90% of the initial thresholdstress value TS1.
 2. The composition of claim 1, wherein the inorganicthixotropic-enhancing metal oxide is added in an amount of between 300ppm and 700 ppm, by weight.
 3. The composition of claim 1, wherein thethixotropic-enhancing metal oxide is selected from CaO, MgO orcombinations thereof.
 4. The composition of claim 1, wherein thecomposition comprises less than 300 ppm by weight of water.
 5. Thecomposition of claim 1, wherein the composition comprises less than 700ppm by weight of water.
 6. The composition of claim 1, wherein thecomposition comprises no water.